The present invention relates in general to the use of electromagnetic acoustic transducers (EMATs) for testing materials and, in particular, to a new and useful method and apparatus for performing non-destructive testing using EMATs which avoids the problem of "main bang," that is, the overloading of the EMAT receiver by the electrical interference created by the high energy transmitter pulse.
In most cases, prior art EMAT testing systems use the same EMAT coil to transmit waves and to receive reflected waves. Resistance was added to the EMAT coil, in some cases, in order to reduce the Q of the tuned circuit, reducing the duration of the main bang or overload signal, but at the same time reducing signal amplitude and signal-to-noise ratio. In other cases separate non-overlapping coils were used to transmit and receive. This can cause problems because the coils are not at the same location for transmitting and receiving.
When performing nondestructive testing using EMATs, there is typically a region adjacent the EMAT from which no reflections can be received due to main bang. Main bang is a large signal in the receiver output created by the transmitter pulse. This is such a large signal that it completely overloads the receiver, preventing it from detecting any reflections during this time. The duration of the main bang includes the length of the transmit pulse, and a period of time immediately after transmitting, during which the transmit pulse decays to a level small enough so that it no longer interferes with the detection of reflections. The duration of the main bang is a significant impediment for many potential applications of EMATs at the present time.